The present invention provides a process to produce a solution blend of a polybenzimidazole (PBI) and a polyetherketoneketone (PEKK) where the process produces a blend in all proportions from 1/99 to 99/1 (PBI/PEKK).
Polybenzimidazoles (PBI) are polymers of high thermal stability and are resistant to oxidative or hydrolytic degradation. Polybenzimidazole polymers may be prepared by melt polymerizing an aromatic tetraamine and a diphenylester or an anhydride of an aromatic or heterocyclic dicarboxylic acid in a one or two-stage process; see, for example U.S. Pat. Nos. Re. 26,065; 3,174,947; 3,509,108; 3,551,389; 3,433,772; and 3,655,632. In particular, U.S. Pat. No. 3,551,389 discloses a two-stage process for the production of aromatic polybenzimidazoles, in which the monomers are heated at a temperature above 170° C. in a first-stage melt polymerization zone until a foamed prepolymer is formed. The foamed prepolymer is cooled, pulverized, and introduced into a second stage polymerization zone where it is heated again to yield a polybenzimidazole polymer product. Polybenzimidazoles also may be prepared from the free dicarboxylic acids or the methyl esters of such acids.
Polyaryletherketone polymers comprise a number of closely related polymers including polyetherketone (PEK), polyetheretherketone (PEEK), polyetheretherketoneketone (PEEKK), polyetherketonetherketoneketone (PEKEKK) and polyetherketoneketone (PEKK). These polymers are moldable, and thus easily formed into usable parts. They exhibit excellent long term oxidative stabilities at elevated temperatures (see U.S. Pat. No. 4,320,224 issued Mar. 16, 1982 for “Thermoplastic Aromatic Polyetherketones”). Of the polyaryletherketones, polyetheretherketone (PEEK) is widely commercially available and has been found to be an excellent thermoplastic molding resin. At ambient temperatures PEEK exists as a solid with crystalline and amorphous phases. The amorphous phase, which comprises 52 to 70% of the polymer softens at of temperatures about 143° C. to 155° C., corresponding to the glass transition temperature, Tg, of the amorphous phase.
The remaining 48 to 30% of the polymer exists as a crystalline phase with a melting temperature, Tm, of about 335° C. which is dispersed in the amorphous phase. The polymer softens when heated above Tg and melts at temperatures above Tm. Unfilled grades of partially crystalline polymers like PEEK are not useful in molded part forms at temperatures much above their Tg since the softening that occurs leads to a sharp loss in polymer mechanical properties, especially stiffness (i.e., modulus). This lowered stiffness is reflected in reduced dimensional stability under stress at temperatures above Tg.
Previous efforts studying the synergistic properties of PBI and polyaryletherketone (PAEK) focused on PAEK polymers with low ketone ratios; primarily PEEK with a 33% ketone ratio and PEK with a 50% ketone ratio. These mixtures do benefit from PBI's ability to immobilize the amorphous regions of the polyaryletherketone matrix resin, thereby imparting enhanced thermo-mechanical properties not obtainable with other fillers of polyaryletherketone, but which fall short of that obtained in a miscible blend of polymers. Examples of these prior efforts can be found in U.S. Pat. Nos. 4,912,176, 5,070,153, 5,391,605, and 5,844,036.